The Yungul carbonatite dykes associated with the epithermal fluorite deposit at Speewah, Kimberley, Australia: Carbon and oxygen isotope constraints on their origin

L. G. Gwalani, K. A. Rogers, A. Demény, D. I. Groves, R. Ramsay, A. Beard, P. J. Downes, A. Eves

Research output: Contribution to journalArticle

16 Citations (Scopus)

Abstract

The Yungul carbonatite dykes at Speewah in the Kimberley region of Western Australia were emplaced along a north-trending splay from the northeast-trending Greenvale Fault located at the western boundary of the Halls Creek Orogen. The Yungul carbonatite dykes intrude a thick composite sill of the Palaeoproterozoic Hart Dolerite (~1,790 Ma), consisting of tholeiitic dolerite and gabbro with its felsic differentiates that form the Yilingbun granophyres and associated granites. The carbonatite dykes consist of massive, calcite carbonatite that host very coarse, pegmatitic veins and pods of calcite, and have largely replaced (carbonatitized) and fenitized the country rock Hart Dolerite suite in a zone up to 150 m wide. Dykes of red-brown siliceous fluidized-breccia and epithermal-textured veins consisting of bladed quartz, adularia and fluorite are closely associated with the carbonatite dykes. The Yungul carbonatites are closely associated with fluorite occurrences with resources currently reported as 6. 7 Mt at 24. 6% CaF2. The precise age of the Yungul carbonatite is not known, although it is believed to be post early Cambrian. The total REE content of the Yungul carbonatite is low (174. 0-492. 8 ppm; La/Yb 2. 28-10. 74) and thus atypical for calciocarbonatite. Chondrite-normalized REE patterns for the carbonatite are relatively flat compared to average calciocarbonatite, and show small negative Eu anomalies. These unusual geochemical features may have been acquired from the Hart Dolerite suite during emplacement of the carbonatite, a process that involved extensive replacement and fenitization of country rocks. Carbon and oxygen isotope compositions of massive calcite carbonatite and the coarse calcite veins and pods from the carbonatite suggest a deep-seated origin. The C and O isotope compositions show an overall positive correlation that can be attributed to both magmatic and magmatic-hydrothermal processes in their evolution. The magmatic δ13C-δ18O trend is also indicative of crustal contamination and/or low-temperature water/rock exchange. The carbon isotopic compositions have δ13C values that range from about -5. 2‰ to -6. 3‰ that support a mantle-derived origin for the Yungul carbonatites and are consistent with earlier conclusions based on whole-rock geochemistry and radiogenic isotopes studies.

Original languageEnglish
Pages (from-to)123-141
Number of pages19
JournalMineralogy and Petrology
Volume98
Issue number1-2
DOIs
Publication statusPublished - Mar 2010

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Oxygen Isotopes
Carbon Isotopes
carbon isotopes
Fluorspar
Calcium Carbonate
carbonatite
oxygen isotopes
fluorite
calcite
carbon isotope
oxygen isotope
Deposits
deposits
veins
Rocks
rocks
Isotopes
isotopes
Chemical analysis
diabase

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geophysics

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The Yungul carbonatite dykes associated with the epithermal fluorite deposit at Speewah, Kimberley, Australia : Carbon and oxygen isotope constraints on their origin. / Gwalani, L. G.; Rogers, K. A.; Demény, A.; Groves, D. I.; Ramsay, R.; Beard, A.; Downes, P. J.; Eves, A.

In: Mineralogy and Petrology, Vol. 98, No. 1-2, 03.2010, p. 123-141.

Research output: Contribution to journalArticle

Gwalani, L. G. ; Rogers, K. A. ; Demény, A. ; Groves, D. I. ; Ramsay, R. ; Beard, A. ; Downes, P. J. ; Eves, A. / The Yungul carbonatite dykes associated with the epithermal fluorite deposit at Speewah, Kimberley, Australia : Carbon and oxygen isotope constraints on their origin. In: Mineralogy and Petrology. 2010 ; Vol. 98, No. 1-2. pp. 123-141.
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abstract = "The Yungul carbonatite dykes at Speewah in the Kimberley region of Western Australia were emplaced along a north-trending splay from the northeast-trending Greenvale Fault located at the western boundary of the Halls Creek Orogen. The Yungul carbonatite dykes intrude a thick composite sill of the Palaeoproterozoic Hart Dolerite (~1,790 Ma), consisting of tholeiitic dolerite and gabbro with its felsic differentiates that form the Yilingbun granophyres and associated granites. The carbonatite dykes consist of massive, calcite carbonatite that host very coarse, pegmatitic veins and pods of calcite, and have largely replaced (carbonatitized) and fenitized the country rock Hart Dolerite suite in a zone up to 150 m wide. Dykes of red-brown siliceous fluidized-breccia and epithermal-textured veins consisting of bladed quartz, adularia and fluorite are closely associated with the carbonatite dykes. The Yungul carbonatites are closely associated with fluorite occurrences with resources currently reported as 6. 7 Mt at 24. 6{\%} CaF2. The precise age of the Yungul carbonatite is not known, although it is believed to be post early Cambrian. The total REE content of the Yungul carbonatite is low (174. 0-492. 8 ppm; La/Yb 2. 28-10. 74) and thus atypical for calciocarbonatite. Chondrite-normalized REE patterns for the carbonatite are relatively flat compared to average calciocarbonatite, and show small negative Eu anomalies. These unusual geochemical features may have been acquired from the Hart Dolerite suite during emplacement of the carbonatite, a process that involved extensive replacement and fenitization of country rocks. Carbon and oxygen isotope compositions of massive calcite carbonatite and the coarse calcite veins and pods from the carbonatite suggest a deep-seated origin. The C and O isotope compositions show an overall positive correlation that can be attributed to both magmatic and magmatic-hydrothermal processes in their evolution. The magmatic δ13C-δ18O trend is also indicative of crustal contamination and/or low-temperature water/rock exchange. The carbon isotopic compositions have δ13C values that range from about -5. 2‰ to -6. 3‰ that support a mantle-derived origin for the Yungul carbonatites and are consistent with earlier conclusions based on whole-rock geochemistry and radiogenic isotopes studies.",
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